The invention relates to a gastight connection between tubes of small diameter of metals or metal alloys having different melting points, wherein the end zone of the first tube is opened out and the end of the second tube is inserted into the opened-out portion, and wherein an originally existing soldering gap between the opened-out portion and the inserted second tube is filled with a material having a lower melting point than the metal or metal alloy.
A connection of the kind specified is publicly known to have been used in the form of an aluminium tube which is opened out at its end and into which a copper tube is inserted. The insertion connection is made with high precision, namely a very narrow soldering gap, to enable the opened-out portion and the pipe end to be directly interconnected under heat without the supply of outside solder. The connection itself is more a diffusion welding connection than a soldered connection.
German OS 1 908 888 discloses another tube connection system wherein the tube ends are indirectly connected via a tube socket with conical insertion ends and wherein an inserted piece of soldering material must always be provided in the soldering gap.
Since the aforedescribed direct connection of a copper tube to an aluminium tube calls for high precision in production, electric butt pressure welding is also still used for connecting the end faces of the tubes of different materials, with the consequent inevitability of the extra production steps of external and internal deburring, flushing out of the internal chips and drying.
Another technical disadvantage of butt pressure welding is that at present adequate production safety demands a tube diameter of 7.5 mm for a wall thickness of approximately 1 mm, although more particularly for such Cu/Al tube connections and their various utilizations a diameter range of at most approximately 6.5 mm would be desirable.
It is an object of the invention to obviate the aforedescribed disadvantages of the prior art and to provide a reliably gastight tube connection between tubes of materials having different melting points, more particularly between a copper tube and an aluminium tube. It is an object of the invention to provide a suitable production process and a corresponding installation for the production of the gastight connection.